1. Field of the Invention
The present invention relates to scrapers for cleaning the working surfaces of conveyor belts, and, more particularly, to conveyor belt scrapers having resilient means to urge scraper blades into the belt surface.
2. Prior Art
Conveyor belt machinery is often used to convey particulate materials which have a tendency to adhere to the working surface of the conveyor belt. For example, in the coal mining industry, it is necessary to wet the chunks of coal transported by conveyor belts in and around coal mines. This is necessary to reduce the amount of airborne coal dust. A consequence of wetting the chunks of coal on the conveyor belts is that the fine coal dust particles become sticky and adhere to the working surface of the conveyor belt. This mud-like accumulation tends to build up on the return idler rollers which support the underside or return flight of the conveyor belt and may tend to jam the rollers and generate dangerously high temperatures which may ignite the coal dust. Thus, it is necessary to employ conveyor belt scrapers to remove the accumulation of wetted particulate matter from these conveyor systems.
There are many types of conveyor belt scrapers in use. For example, U.S. Pat. No. 3,999,649 is directed to a conveyor belt scraper having an axle rotatably mounted to a support located proximate the return flight of a conveyor belt, a pair of primary arms attached to and extending outwardly from the ends of the axle and supporting a conterweight, and a pair of secondary arms extending from the ends of the axle and suppporting a blade assembly which engages the belt. The counterweight is positioned so that it causes the axle to rotate thereby urging the blade assembly upward into the return flight of the belt.
Similarly, U.S. Pat. No. 1,875,442 discloses a belt scraper having a fulcrum mounted beneath the return flight of the conveyor belt, and a U-shaped lever arm attached to the fulcrum. At the ends of the U-shaped lever arm a pair of weights are mounted causing the opposite portion of the lever arm to be urged upwardly into the return flight of the conveyor belt. A series of blades are mounted on the opposite portion of the lever arm and are positioned to engage the belt when the lever arm is pivoted about the fulcrum. The blades are disposed at an angle with respect to the travel of the lever arm thereby urging accumulated material off to one side in much the same fashion as the action of a snow plow.
A disadvantage with these types of belt scrapers is that they rely on gravity to urge the scraper blade or blades into the conveyor belt. Thus, the positioning of the scraper blades is severly limited; the apparatus must be positioned such that the counterweight may rotate the blade arm about a fulcrum or axle upwardly into the belt. An additional disadvantage is that uneveness in that belt or the rollers may cause the blade to bounce away from the belt, thereby leaving portions of the belt unscraped and allowing the accumulated material on those portions to adhere to idler rollers downstream of the scraper.
A second type of conveyor belt scraper is disclosed in U.S. Pat. No. 2,393,724. This scraper includes a central axle, a lever arm mounted to an end of the axle and extending outwardly therefrom, and a U-shaped blade mount attached to the axle and extending outwardly therefrom. The lever arm slidably engages a rod mounted to the conveyor frame which carries a coil spring. The coil spring extends between the end of the lever arm and a stop such that it causes the lever arm to move away from the stop thereby rotating the axle which causes the blade assembly to rotate upwardly into the conveyor belt. A disadvantage with this type of belt scraper is that it does not counteract "chatter" of the scraper which may occur when the scraper encounters small lumps stuck to the belt. In addition, it is necessary for the rod on which the spring is mounted to be attached to a bar which is rigidly mounted to a portion of the conveyor belt frame. This limits the positioning of the belt scraper apparatus with respect to the belt.
Accordingly, there is a need for a conveyor belt scraper which includes a means for urging the scraper blade or blades into the belt without the use of burdensome counterweights, a belt scraper which can be positioned in a variety of locations relative to the conveyor belt, and a scraper which minimizes chatter of the scraper blade as it encounters larger chunks of material adhering to the belt.